I mainly use Bitcoin Core for sending and receiving Bitcoins.
Is it bad idea to use Bitcoin Core for the main wallet? I don't trust any online exchanges, that require my private keys.
Thanks,
Why don't you use an Electrum wallet instead of bitcoin core. Unless you are some sort of techy person or a developer, you do not need to download the whole database on your system.
I think Electrum is as good as Bitcoin core wallet but if you want to completely secure your wallet, you better go for the hardware wallets.
BTC stored in any wallet can be lost if the owner doesn't have good operational security, it doesn't matter if it is BTC core, Electrum, BlueWallet or any other wallet. Hot wallets can be hacked, so cold wallets are safer than hot wallets, but in either of them if your seed phrase is exposed, the funds would be lost. If you know how to store and use your funds in a safe enviroment, the chances of losing it is very low.
If you lose your seed phrases or expose your seed phrases to anyone, then the wallet security has nothing to do with any mishap, it is your own carelessness which may lead to the loss of funds from your wallet.